FreeMCATPrep Logo

More Than 475 Free MCAT Questions with Detailed Answers!

Click HERE for your Random Question from our MCAT Question A Day Archive

General Chemistry - Kinetic Molecular Theory

The kinetic molecular theory states that for ideal gases:
  1. The kinetic energy of a gas is directly proportional to its absolute temperature, so the greater the temperature, the greater the kinetic energy.
  2. Compared to the volume of the space that the particles move in, the volume of gas particles is small.
  3. No forces of attraction occur between the particles, so when a collision takes place, there is no loss of kinetic energy.
  4. The time between collisions is significantly larger than the time during collisions.

Units of Pressure :
760 torr = 760 millimeters of mercury = one atmosphere = 1.013 × 105 pascals

We measure pressure using a barometer. For gases, the standard temperature and pressure (STP) means 0° degrees Celsius (C) and one atmosphere. Remember that at STP, a mole of any gas will take up 22.4 liters of volume. For ideal gases, pressure and temperature are directly proportional.

Rule Number 8:
Initial pressure / initial temperature = final pressure / final temperature (P1/T1 = P2/T2)

If the temperature remains constant, then pressure is inversely related to volume.

Rule Number 9: Boyle’s Law

Initial pressure × initial volume = final pressure × final volume (P1V1 = P2V2)

Now, if the pressure is kept constant, the volume is directly related to the temperature.

Rule Number 10: Charle’s Law

Initial volume / initial temperature = final volume / final temperature (V1/T1 = V2/T2)

If we combine Boyle’s law with Charles’s law, we get rule 11.

Rule Number 11: Combined Gas Law

Initial pressure × initial volume / initial temperature = final pressure × final volume / final temperature (P1V1/T1 = P2V2/T2)

Rule Number 12: Ideal Gas Law

Pressure × volume = number of moles × ideal gas law constant × temperature (PV=NRT)

The ideal gas law constant is 0.0821 liters atmosphere per moles Kelvin. You’ll be given this number so you don’t need to memorize it. You may be asked to compare the speeds of two gas molecules in a closed container. You can do this by using Graham’s law.

Rule Number 13:
v1 / v2 = √ (m2 / m1); v is the velocity and m is the mass of each molecule.